1. Field of the Invention
The invention relates to methods and systems for the separation of halogenated alkane streams from heavy ends. In particular, the invention is directed to the separation of 1,1,1,3,3-pentachloropropane from the heavy ends produced in the formation of 1,1,1,3,3-pentachloropropane.
2. Description of the Related Art
Fluorocarbon producers have actively pursued the production of fluorocarbons to replace the banned chlorofluorocarbons (CFC""s). These fluorocarbons will require hydrochlorocarbon feedstocks.
Several fluorochemical producers have targeted fluorocarbon 1,1,1,3,3-pentafluoropropane, utilizing 1,1,1,3,3-pentachloropropane as the feedstock, as the primary replacement product for foam blowing Zil""bennan et al. (xe2x80x9cSynthesis of liquid telomers of vinyl chloride with carbon tetrachloride,xe2x80x9d J. Org. Chem. USSR (English Transl.), 3:2101-2105, 1967) prepared 1,1,1,3,3-pentachloropropane in a 58% yield by the reaction of carbon tetrachloride (CCl4) and vinyl chloride using ferrous chloride tetrahydrate in isopropanol. In addition, Kotora et.al. (xe2x80x9cAddition of tetrachloromethane to halogenated ethenes catalyzed by transition metal complexes,xe2x80x9d J Mol. Catal., 77(1):51-60, 1992) prepared 1,1,1,3,3-pentachloropropane in high yields using either cuprous chloride/butylamine or tris(triphenylphosphine)dichlororuthenium.
European Patent Application No. 131561 describes a very general process for the addition of a haloalkane compound to an alkene or alkyne compound in the presence of iron metal and a phosphorus (V) compound to form halogenated alkanes. EP 131561 sets forth several examples of the batch reaction of ethylene and carbon tetrachloride to produce 1,1,1,3-tetrachloropropane. EP 131561 also mentions a wide variety of other olefins and alkynes, including vinyl halides. It states that the batch process could be made continuous, but does not include any specific information concerning how this would be carried out.
U.S. Pat. No. 6,187,978 describes a process based on Kharasch chemistry where polyhalogenated alkanes and olefins are reacted in the presence of a transition metal catalyst. The reaction results in the following Kharasch reaction:
CCl4+CH2=CHClxe2x86x92CHCl2xe2x80x94CH2xe2x80x94CCl3(1,1,1,3,3-pentachloropropane)
U.S. patent application Ser. No. 09/671,993 filed Sep. 29, 2000 now allowed, describes a process which includes a reaction step, a catalyst recovery step, and a process to purify the haloalkane product. In the process, a portion of the catalyst stream is withdrawn from the catalyst recovery unit and is disposed of as a waste stream in order to prevent the build up of unreactive by-products. The waste stream can contain up to 50 weight percent of 1,1,1,3,3-pentachloropentane product. Thus, the volume of product in the waste stream constitutes a significant loss of feed conversion to the desired product.
Conventional distillation and even low temperature distillation of waste streams has resulted in decomposition of both the 1,1,1,3,3-pentachloropropane product and catalyst components in the waste stream. Tar-like by-products, which foul the equipment, for example, are formed. Likewise, treatment of waste streams by performing a combination of solvent and aqueous extraction is ineffective and costly. Generally, a primary aqueous extraction is followed by the addition of non-polar solvents to separate the waste stream into two phases. These phases can then be further separated to recover the reactants. However, tests have demonstrated that extractions through the employment of aqueous, or aqueous plus inorganic salts and/or acids, or aqueous plus polar solvents, were ineffective in extracting iron, useful reactants and products. Aqueous based extractions induce precipitation of solids, which in turn require increased waste handling and waste disposal costs.
To meet the requirements of the fluorocarbon industry of providing a pure fluorocarbon feedstock at a high yield and to overcome the disadvantages of the related art, it is an object of the present invention to provide a novel method for separating heavy ends from a halogenated stream in a facile and cost-effective manner.
It is another object of the invention to recover from the waste stream a halogenated alkane stream, which contains desirable halogenated alkane(s) leaving a heavy ends stream that is disposed of as a waste product. The recovered halogenated alkane stream that can be further purified to give a product for use as a fluorocarbon feedstock.
It is another object of the invention to employ steam in the separation of the heavy ends from the waste stream and to recover the steam as a water phase, which will then be utilized to treat additional waste stream.